This invention relates to heating of SiO.sub.2 -based material in the semiconductor art.
The phosphosilicate glass flow process is used primarily to round off sharp edges of etched cuts on phosphosilicate glass to help prevent cracking at the edges of subsequently deposited metal or polycrystalline silicon fill and also to smooth the overall surface of a layer of phosphosilicate glass for subsequent controlled etching thereof. The flow process is normally induced by high temperature (approximately 950.degree. C. or above) furnace anneal.
In general, the phosphosilicate glass layer is part of a structure initially formed by providing a silicon substrate with a thermally deposited silicon dioxide (SiO.sub.2) layer thereon. A layer of P.sub.2 O.sub.5 -SiO.sub.2 is then chemically vapor deposited on the layer of thermally deposited SiO.sub.2 by, for example, reaction of a phosphorous-silane mixture and oxygen at low temperature, so that a top layer of phosphosilicate glass is provided.
A major problem with the prior art approach of inducing flow by high temperature anneal is that when device structures, i.e., structures which may be of material in close proximity to the phosphosilicate glass, are heated to a relatively high temperature in the furnace, their properties often undesirably change due to dopant diffusion, alloying and contamination. Another problem is that P.sub.2 O.sub.5, typically in the concentration of 7-9 mol %, must be added to the SiO.sub.2 base composition to lower the flow temperature. This subsequently enhances corrosion of the metal interconnections.